Wednesday, October 31, 2007

It seems many aspects of Ron Pittaway's Winter Finch Forecast are well vetted already, before winter has even begun. Winter finches are invading! Ron predicted southward irruptions out of Ontario of Evening Grosbeak, Pine Siskin, Redpolls, Bohemian Waxwings, and more. Many of these species have already been seen in numbers in the Cayuga Lake Basin or nearby.

Matt Young summarizes the invasion so far in a post on cayugabirds-l:

Pine Grosbeaks in small numbers in most NE state --Mass(1 ind), ME, VT, NH and NY; Bohemian Waxwings in widespread numbers from most NE states(only an ind from Mass); Common Redpoll in every NE state except Vermont, Conn. RI(including a sighting in Cortland); Pine Siskins and E. Grosbeaks in numbers from Ontario to Carolinas; Shrikes are moving in good numbers too; Boreal Chickadees and Black-backed Woodpeckers moving; and some indication of hawks and owls moving as well. Lets hope many linger in NY. Should be interesting.

I think the story of this invasion so far is how widespread and early the Bohemian Waxwings are. They can be found in numbers in ME, VT, NH, NY and it's still October. Could they be the next Evening Grosbeak?

Here in the Basin, Evening Grosbeaks have been present (although enigmatic, rarely staying in one place for more than one day) for several weeks. Pine Siskins have been present in larger numbers and have put on a good show for many local birders. Northern Shrikes have been reported already several times. Lapland Longspurs have been an enigmatic presence since as early as September, and Snow Buntings are now being reported. Bohemian Waxwings haven't reached the Basin yet, but Matt Young reports on them in NY from another cayugabirds-l post:

Don't know for sure if this is still accurate(I think it is though), but according to Bull's Birds of NY the earliest previous record for Bohemian Waxwing was October 28th, thus making Jeff Bolsinger's Fort Drum bird on Oct 24th the new early date. Also, Dave Wheeler's 10 Bohemian Waxwings in Wayne County on Oct 25 and Matt Medler's 49 in Willsboro today (Oct 28th) are also early. Bohemian Waxwings have now been recorded in NY, Vermont, NH and Maine. An annual fall Ontario bird count recorded a record 169 Bohemian Waxwings today. Evening Grosbeaks and Pine Siskins are widespread and reported from all NE states. Pine Grosbeaks have been reported in Maine, NH, and Vermont. 100's of Common Redpolls and now 4 Hoary Redpolls were reported from a banding station in Michigan today. Common Redpoll has also been reported from Penn, NY, Mass and Maine. Flocks of both crossbills can still be found here and there.

And, in the last two days 2 Boreal Chickadees and a Gray Jay were reported from Massachusetts, a state this normally resident species does NOT breed in. And lastly, numbers of Black-backed woodpeckers have been seen flying south past observation points to the north.

Things are looking interesting.

Interesting, indeed. Another species has been present recently in the Basin: Red Crossbill. This one bred over the summer near the Basin to the East, so is not unusual. What could prove interesting is an analysis of the call type and comparison to the call type(s) that were breeding in the area. Saw-whet Owls are also having an excellent migration according to banders.

You may have noticed I used an icon in my latest post on Ammodramus indicating I was blogging on peer-reviewed research.

This icon is part of a toolset developed by BPR3 (Bloggers for Peer-Reviewed Research Reporting), complete with guidelines for use. Clicking the icon provides a link to a list of all the other bloggers writing about peer-reviewed research, providing a two-way database. I think the idea is great, and will use it in all future posts where I talk in detail about peer-reviewed articles. The icon will cue you in that I am not just spewing my mouth off, but am trying to make a quality post on some subject. We'll see how it goes.

Six full months of blogging has gone by (hard to believe!), and it is fitting that I reached a milestone this month: first month with over 1000 views. Of course PZ at Pharyngula gets to celebrate his million visit month, but hey, everyone starts small. Its been a fun time - you can certainly expect more from me. :)

David Sibley has a great post summarizing the records of Green-breasted Mango in the US - up to 19 records now. This makes me wonder... do you think the increasing rate of records is due to increased vigilance or an actual increase in the vagrancy of the bird? Something to ask about all of our rarity records. I'm positive this discussion has taken place many times before, if anyone knows some good links on the topic, chime in.

Tuesday, October 30, 2007

Following up on my previous posts on Nelson’s Sharp-tailed Sparrows and the difficulties in their identification to subspecies, I looked into the systematics and taxonomy of the Sharp-tailed Sparrow group. Nelson’s Sharp-tailed Sparrow (consisting of Ammodramus nelsoni nelsoni, A. n. alterus, and A. n. subvirgatus) and Saltmarsh Sharp-tailed Sparrow (A. caudacutus caudacutus and A. c. diversus) were split from the former lump species Sharp-tailed Sparrow (A. caudacutus) in 1995 by the 40th Supplement to the AOU Check-list of North American Birds (Auk 112(3): 819-830. 1995) with the following reasoning (pg 826):

Split Ammodramuscaudacutus to A. caudacutus and A. nelsoni, following Greenlaw (1993), who found that the two groups of populations differ in song, morphology and habitat, with limited interbreeding at a secondary contact zone in southern Maine. Although Rising and Avise (1993) suggested retaining these two taxa as subspecies of caudacutus, they do not interbreed freely and should be ranked at the species level.

I crudely chopped together this figure from these sources: Rising’s Sparrow Guide and BNA Account. See also the figures in my previous post.

See also these specimen comparisons from Tom Johnson: dorsal and ventral comparisons.

Although they were the later of the two publications, I’ll start with Rising and Avise (1993). Rising and Avise (1993) followed up on the discovery in an earlier paper on the systematics of Ammodramus (Zink and Avise 1990) that there were two distinct mitochondrial genotypes in A. caudacutus (pre-split). They collected a series of 220 specimens from all populations and analyzed the mtDNA of 107 of those with restriction endonucleases (a technique now replaced by sequencing; this paper is old enough that they refer to this as “phylogeography” in quotes). The results indicated two distinct, strongly supported clades of Sharp-tails. The clades divided the populations into what are now Nelson’s and Saltmarsh, with two exceptions: a locale in Maine where the mtDNA from both species occurred with equal frequency, and a locale in Massachusetts where about one bird in five had some Nelson’s mtDNA.

The authors examined the phenotypes of the introgressed individuals:

As you can see, all birds with southern (Saltmarsh) mtDNA had southern plumage, while some of the birds with northern (Nelson’s) mtDNA had southern plumage. mtDNA is passed down by female lineage, so from this discordance in the plumage vs. genetics, the authors conclude that there is differential mate preference in the contact zone: southern females prefer southern males, while northern females show no selectivity. This would allow the introgression of southern males and their plumage characters into the northern mtDNA ‘population’. The authors hypothesize that this is due to larger southern males outcompeting smaller northern males.

In sum, the authors discover a distinct mtDNA split, a distinct division in morphological characters examined, and a contact zone with asymmetrical hybridization. The authors take the taxonomically conservative stance of maintaining one Sharp-tail species, but giving the Nelson’s and Saltmarsh divisions subspecies rank, subsuming the previous subspecific variation. They argue against splitting until stronger evidence of intrinsic reproductive barriers is found.

One pre-zygotic (before mating) reproductive barrier is behavioral differences. Greenlaw (1993) added to the study of Sharp-tails with behavior and morphological examinations across the contact zone. Saltmarsh subspecies sing what he describes as a ‘complex whisper song’ with no display, whereas Nelson’s sing a different song and an accompanying flight display.

His analysis of behavior and morphology characters showed no gradient of change northward up the coast, instead representing an abrupt shift in the same contact zone in Maine (Popham Beach) as sampled in Rising and Avise (1993). Even more interesting, the two types coexist together in that contact zone. The same stepwise transition occurs in habitat type: tidal saltwater marshes in the south to brackish less-tidal marshes in the north.

Combining these two studies, we get populations distinct in: genetics, plumage, morphology, behavior, voice, and habitat, - and coexisting with a small level of introgression in a narrow band in Maine. The exact barriers to reproduction between the two forms are not known, but these studies suggest it is a form of behavioral isolation involving different song types and displays. Indeed, the sympatric presence of the two forms with some asymmetric gene flow is evidence of assortative mating – an indication of species-level differences. Putting this evidence together, despite a more detailed study of the contact zone lacking, was enough for the AOU to consider the two as separate species.

References:

40th Supplement to the AOU Check-list of North American Birds (Auk 112(3): 819-830. 1995)

James D. Rising. A Guide to the Identification and Natural History of the Sparrows of the United States and Canada. 1996

James D. Rising and John C. Avise. 1993. Application of genealogical-concordance principles to the taxonomy and evolutionary history of the sharp-tailed sparrow (Ammodramus caudacutus). The Auk. 110(4): 844-856.

Monday, October 29, 2007

This weekend was the Arnot Teaching Forest weekend field trip. This wonderful expanse of land run by our Natural Resources Department sits in a little pocket of Schuyler county, 30 minutes southwest of Cornell, and hosts a big Sugarbush providing Cornell's maple syrup production. Mmm... maple syrup... but I digress.

This weekend, our class was instructed in many field techniques, including clinometry, compass work, using topographic maps, herping, and field sampling. The crux of the whole trip was intensive small mammal trapping. We split into three groups, running Sherman live trap lines in three locations: the sugarbush, creekside, and an old field at the top of the big hill. I immediately volunteered to take my group up to the old field, because the big fields hold some nice views and good herping (at least in the summer, when it is warmer than 50 degrees).

Organizing and baiting the traps

I took my group on a bouncy, rough ride in the van up to the old fields. It was still early morning, cold, wet, and clouds were clinging to the top of the hill:

We set up a trap line of 50 traps spaced five meters apart. We tried to make it as straight as possible, but still ended up with a weaving line through the field and brush. "If this were a real study, we would make the line straight..."

Interesting finds on this early morning walk that left us soaked from the waist down from dew:

A very cold and nonmoving Garden Spider

Perhaps the most proudly displayed box of Coyote scat ever

We returned to the lodge, tried to dry ourselves off by the fireplace, then began our days activities. Our three groups rotated between three activities: mapping, orienteering, and herping (led by me!).

I did a loop with each group, covering multiple specific habitat types: field, forest floor, marshy pond edges, vernal pool, rocky slope, and creek. It worked quite well, and was able to have them find a variety of species of salamander, most other herps having been burrowing in for the winter with the recent cold. Some highlights from our woodland walks:

Me teachin' (Photo by Chris Bentley)

A slug exuding slime where someone touched it.

A decent sized spider dropping down from the trees. Look near the bottom of the pic for it hanging. You couldn't feel the silk thread, but grabbing at where it should be allowed us to pass the spider around.

When the spider hit the ground it curled up.

A very nice patch of lichen and sporulating Lycopodium.

Another class had this bridge collapse while they crossed it a week ago.

(Photo by Chris Bentley)

After the days activities were all through, we made another quick run at dusk to the old field to check the trap line. We came up empty mammal-wise, but we had gunning the van through expanses of puddle on the road and got some nice views of the setting sun lighting up the fall foliage on the hills.

The rest of the night was taken up by dinner, after-dark trap checks (cold and blustery on the hilltop!), s'mores, and bonfire (naturally).

Marshmallow fun(Photo by Chris Bentley)

The next day, we collected the traps (closed during the night to prevent further capture) and had the groups summarize and present their findings.

Red-backed Vole - Adorable. They huddle together in a pile and sound like squeeky toys.

We did fairly well on birds too. We added a new species to the Arnot checklist - Red-bellied Woodpecker. We also heard a Fox Sparrow singing in the exact spot we mist-netted one two years ago. Mitch heard some Pine Siskins, and Raven were flying around all day.